when a waiter or bartender is working in a very loud bar or restaurant and cannot completely hear what the customer is saying but they start to laugh when they thought it was a time to insert laughter.
also known as a courtesy laugh when a customer says something at all remotely funny so you use the waiter laugh or bartender laugh to make the customer think they are funny.

I was table-side when the family was talking to me and I started using my "courtesy (waiter laugh or bartender laugh) laugh" when Mr. Young told the same story he has told 45 times previously.